1. Technical Field
The present invention relates to novel monoclonal antibodies which may be used in the detection of Human Immunodeficiency Virus (HIV). These antibodies exhibit an unusually high degree of sensitivity, a remarkably broad range of specificity, and bind to novel shared, non-cross-reactive epitopes. In particular, the monoclonal antibodies of the present invention may be utilized to detect HIV-1 antigen and HIV-2 core antigen in a patient sample.
2. Background Information
Acquired Immunodeficiency Syndrome (AIDS) is an infectious and incurable disease transmitted through sexual contact from HIV infected individuals or by exposure to HIV contaminated blood or blood products. HIV-1 includes the formerly named viruses Human T-cell Lymphotrophic Virus Type III (HTLV III), Lymphadenopathy Associated Virus (LAV), and AIDS Associated Retrovirus (ARV). HIV is a retrovirus related to a group of cytopathic retroviruses, namely lentiviruses, on the basis of morphologic features, genomic organization, and nucleotide sequence (Gonda et al., Science (1985) 277:177-179; Stephan et al., Science (1986) 231:589-594; Korber, B. (ed.) et al., Human Retroviruses and AIDS. A Compilation and Analysis of Nucleic Acid and Amino Acid Sequences. Published by Theoretical Biology and Biophysics, Los Alamos National Laboratory, Los Alamos, N. Mex.; Reviewed in, Schochetman, G. and George, J. R., (1994) AIDS Testing. Springer-Verlag, New York, Berlin, Heidelberg). HIV is an enveloped virus containing several structural proteins. Of particular relevance, the core of the virus is formed by condensation of cleavage products from a highly processed gag-pol polyprotein precursor (Pr180gag-pol) which is cleaved into a pol precursor and a gag precursor (Pr55gag). Subsequently, the core precursor Pr55gag is cleaved into p17 (myristilated gag protein), p24 (major structural protein), p7 (nucleic acid binding protein), and p9 (proline-rich protein). The envelope contains two structural proteins, gp120 (envelope glycoprotein) and gp41 (transmembrane protein) which are cleavage products of the envelope polyprotein precursor, gp160.
The most common markers of HIV infection are antibodies against viral structural proteins (Dawson, et. al., J. Infect. Dis. (1988) 157:149-155; Montagnier, et al. Virology (1985) 144:283-289; Barin, et al., Science (1985) 228:1094-1096; Schulz, T. F., et al., Lancet (1986) 2:111-112; Sarngadharan, et al., Science (1984) 224:506-508; Allan, et al., Science (1985) 228:1091-1093) and viremia in the form of detectable viral core antigen (antigenemia) (Kessler, et. al., JAMA (1987) 258:1196-1199; Phair, JAMA (1987) 258:p1218; Allain, et al., The Lancet (1986) ii: 1233-1236; Kenny, et al., The Lancet (1987) 1 (8532):565-566; Wall, et al., The Lancet (1987) 1(8532):p566; Stute, The Lancet (1987) 1(8532):p566; Goudsmit, et al., The Lancet (1986) ii: 177-180; vonSydow, et al., Brit. Med. J. (1988) 296:238-240; Bowen, et al. Ann. of Int. Med. (1988) 108:46-48) or detectable viral nucleic acid (Mellors, et al., Science (1996) 272: 1167-1170; Saag, et al. Nat. Med. (1996) 2: 625-629; Mulder, et al. J. Clin. Microbiol. (1994) 32:292-300; Zhang, et al., AIDS (1991) 5(6):675-681; Simmonds, et al., J. Virology (1990) 64(2):864-872). For example, in the United States, screening of blood and blood products by tests to detect antibody or antigen is mandated (Federal Food, Drug, and Cosmetic Act, 21 U.S.C.  301 et. seq., Public Health Service Act 42 U.S.C.  201 et. seq.). Nucleic acid testing recently has been implemented in order to attain maximal reduction of the HIV seroconversion window (www.fda.gov). As a further example, various countries in Europe have begun to evaluate and use tests that detect antibody and antigen simultaneously (Ly, et al. J. Clin. Microbiol. (2000) 38(6): 2459-2461; Gurtler, et al., J. Virol. Methods (1998) 75: 27-38; Weber, et al., J. Clin. Microbiol. (1998) 36(8): 2235-2239; Courouce', et al., La Gazette de la Transfusion (1999) N° 155-Mars-Avril; Van Binsbergen, et al., J. Virol. Methods (1999) 82: 77-84), in addition to European implementation of nucleic acid testing. Serologic assays that combine antibody and antigen detection exhibit superior seroconversion sensitivity compared to assays that detect only antibody, because detection of antigen, which appears prior to antibody, reduces the seroconversion window. An early version of an HIV combo assay is described in Gallarda, et al., 1992, WO93/21346, Assay for Detection of HIV Antigen and Antibody.
Within several weeks after infection with HIV, individuals generally enter a clinical phase characterized by extensive viremia and acute symptoms. During this period, prior to seroconversion, HIV p24 core antigen can be detected transiently in serum or plasma specimens (antigenemia) (Devare, et al., (1990) In, Human Immunodeficiency Virus Innovative Techniques. Monograph in Virology, J. L. Melnick (ed.), Basel, Karger, vol 18: 105-121; Kessler, et al. JAMA (1987 258: 1196-1199; Phair, J. P., JAMA (1987) 258: p1218; Allain, et al. The Lancet (1986) ii: 1233-1236; Kenny, et al., The Lancet (1987) 1(8532): 565-566; Wall, et al., The Lancet (1987) 1(8532): 566; Stute, R., The Lancet (1987) 1(8532): 566; Goudsmit, et al., The Lancet (1986) ii: 177-180; vonSydow, et al., Brit. Med. J. (1988) 296: 238-240; Bowen, et al., Ann. of Int. Med. (1988) 108: 46-48). After seroconversion, the core protein apparently is bound up by antibodies in circulating immune complexes, making core protein detection difficult and requiring immune complex disruption techniques (Schupbach, et al., AIDS (1996) 10:1085-1090; Kageyama, et al., J. Virol. Methods (1988) 22: 125-131; Mathiesen, et al., J. Virol. Methods (1988) 22: 143-148; Steindl, et al., J. Immunol. Methods (1998) 217: 143-151; Euler, et al., Clin. Exp. Immunol. (1985) 59: 267-275; Gupta, et al., New Eng. J. Med. (1984) 310: 1530-1531; Griffith, et al., J. Clin. Microbiol. (1995) 33: 1348-1350). After the initial viremic phase and throughout the remainder of the disease, the virus generally establishes a steady state level (reviewed in Coffin, J. M. Science (1995) 267: 483-489).
Core proteins from isolates of HIV-1 group O, HIV-1 group M, and HIV-2 are antigenically similar because they share regions of amino acid sequence homology. Human (or mouse) immune polyclonal sera (i.e., immunoglobulin) elicited against the core protein of one group or type will cross react against the core protein of a different group or type (Clavel, et al., Science (1986) 233; 343-346; Guyader, et al., Nature (1987) 326: 662-669; Barin, et al., Lancet (1985) 2: 1387-1389; Kanki, et al., Science (1986) 232: 238-243; Kanki, et al., Science (1987) 236: 827-831; Clavel, et al., Nature (1986) 324: 691-695; Hunt, et al., AIDS Res. Human Retroviruses (1997) 13: 995-1005; Gurtler, et al., J. Virol. Methods (1995) 51: 177-184; Mauclere, P. AIDS (1997) 11: 445-453). However, in contrast to human (or mouse) immune polyclonal sera, mouse or human monoclonal antibodies raised or elicited against the core protein of one HIV group or type may (Mehta, et al., U.S. Pat. No. 5,173,399; Butman, et al., U.S. Pat. No. 5,210,181; Butman, et al., U.S. Pat. No. 5,514,541) or may not (Mehta, et al., U.S. Pat. No. 5,173,399; Butman, et al., U.S. Pat. No. 5,210,181; Butman, et al., U.S. Pat. No. 5,514,541) react against the core protein of a different HIV group or type. Often, however, neither cross-reactivity nor shared reactivity (Tijssen, 1993 In, Laboratory Techniques in Biochemistry and Molecular Biology. R. H. Burdon and P. H. van Knippenberg, eds. Vol. 15. Elsevier, Amsterdam) of mouse monoclonal antibodies have been considered or taught (Kortright, et al., U.S. Pat. No. 4,888,290; Kortright, et al., U.S. Pat. No. 4,886,742). In cases where HIV-1 and HIV-2 core proteins were detected simultaneously (Butman, et al., U.S. Pat. No. 5,210,181; Butman, et al., U.S. Pat. No. 5,514,541), a combination of at least 3 monoclonals were required, and the resulting quantitative sensitivity against HIV-1 core protein was much greater (50-fold) than for HIV-2 core protein, indicating that the monoclonals identified cross-reactive epitopes and not shared epitopes. Typically, monoclonal antibodies display a lower affinity against cross-reactive antigens (epitopes) (Karush, F. (1978) In, Comprehensive Immunology, ed. R. A. Good, S. B. Day, 5: 85-116. New York/London: Plenum; Mariuzza, et al., Rev. Biophys. Biophys. Chem. (1987) 16: 139-159; Tijssen, (1993) In, Laboratory Techniques in Biochemistry and Molecular Biology. R. H. Burdon and P. H. van Knippenberg, eds. Vol. 15. Elsevier, Amsterdam) compared to the affinity against the immunizing antigen (epitope) or shared epitope, resulting in less sensitivity toward the cross-reactive antigen.
Shared epitopes are not readily identified, particularly within proteins of related but different sequence. A single amino acid change within an epitope can destroy or modify binding of a monoclonal antibody to that epitope (Mariuzza, et al., Rev. Biophys. Biophys. Chem. (1987) 16: 139-159). In addition, within proteins, amino acid changes (or differences) in sites outside of the epitope can change the epitope due to changes in protein folding (Mariuzza, et al., Rev. Biophys. Biophys. Chem. (1987) 16: 139-159; Layer, et al., Cell (1990) 61: 553-556), thus altering the binding of an antibody to the epitope. In this regard, the core proteins of HIV-1 Group M, HIV-1 Group O, and HIV-2 are related but not identical (Korber, ibid), and although it is known that cross-reactive epitopes exist between HIV core proteins, it is neither certain nor taught that shared epitopes are present.
The extensive genetic (and therefore antigenic) variability of HIV has not been predicted, although many scientific papers have sought to supply explanations for the mechanism(s) of variability (Meyerhans, et al., Cell (1989) 58: 901-910; Wain-Hobson, Curr. Top. Microbiol. Immunol. (1992) 176:181-193; Holland, et al., Curr. Top. Micorbiol. Immunol. (1992) 176: 1-20; Gao, F. et al., Nature (1999) 397: 436-441; Sharp, et al., Biol. Bull. (1999) 196: 338-342; Robertson, et al., Nature (1995) 374: 124-126; Zhu, J. Virol. (1995) 69: 1324-1327). Determination of HIV genetic (and therefore antigenic) variability has relied solely on many empirical observations that subsequently have led to phylogenetic classification based on variation of HIV nucleic and amino acid sequence (Korber, ibid). Similarly, prediction of shared epitopes between HIV (core) proteins cannot be made because (a) core protein sequences must first be discovered, (b) once discovered, genetic variation provides added complexity and uncertainty to the identification of shared epitopes and (c) epitope discovery and characterization are required to differentiate cross-reactive from shared epitopes. Shared epitopes between HIV-1 Group M, HIV-1 Group O, and HIV-2 could not be determined until the discovery of HIV-1 Group O in 1994 (Gurtler, et al., J. Virol. (1994) 68: 1581-1585; Haesevelde, et al., J. Virol. (1994) 68: 1586-1596; Charneau, et al., Virology (1994) 205: 247-253).
The role of monoclonal antibody affinity for equivalent quantitative detection of variable HIV core proteins generally has not been taught (Mehta, et al., U.S. Pat. No. 5,173,399; Gallarda, et al. WO93/21346; Zolla-Pazner, et al., U.S. Pat. No. 5,731,189; Mestan, et al., EP 0519866A1; Butman, et al., U.S. Pat. No. 5,210,181; Butman, et al., U.S. Pat. No. 5,514,541; Kortright, et al., U.S. Pat. No. 4,888,290; Kortright, et al., U.S. Pat. No. 4,886,742). An average affinity for a monoclonal antibody elicited against a protein antigen is 4.5×107 mol−1 (Mariuzza, et al., Rev. Biophys. Biophys. Chem. (1987) 16: 139-159; Karush, F. (1978) In, Comprehensive Immunology, ed. R. A. Good, S. B. Day, 5: 85-116. New York/London: Plenum). Additionally, immunization strategies to increase the probability of obtaining monoclonals against shared epitopes have not been taught.
Only by combining two unpredictable features of monoclonal antibodies, affinity and shared reactivity, can one reasonably expect to obtain monoclonal antibodies which can be used to detect equivalent amounts of related but non identical HIV core proteins. Simple cross-reactivity of monoclonal antibodies is likely to be insufficient to achieve equivalent quantitative detection of HIV core proteins. Rather, shared reactivity in combination with high affinity is required to achieve the desired result. The affinity of a monoclonal for a related core protein may be substantially lower than that determined with the immunizing core protein. In that case, the epitope is most likely cross-reactive and the affinity of the antibody for the cross-reactive epitope may severely limit the utility of the antibody for detection of diagnostically relevant (i.e., 25 pg p24/ml serum or plasma, Courouc., et al., La Gazette de la Transfusion (1999) N° 155-Mars-Avril) concentrations of the cross reactive core protein.
There are currently no known descriptions of immunoassays using only 2 monoclonal antibodies to achieve equivalent quantitative detection of HIV-1 Group M, HIV-1 Group O, and HIV-2 core proteins. Thus, such an immunoassay is certainly desirable. Two or more monoclonals in combination with polyclonal sera (immunoglobulin) have provided the basis for immunoassays to detect HIV-1 core protein or simultaneously HIV-1 and HIV-2 core proteins (Mehta, et al., U.S. Pat. No. 5,173,399; Butman, et al., U.S. Pat. No. 5,210,181; Butman, et al., U.S. Pat. No. 5,514,541; Kortright, et al., U.S. Pat. No. 4,888,290; Kortright, et al., U.S. Pat. No. 4,886,742; Gallarda, et al. WO93/21346). Thus, in view of the above, previous literature fails to (a) describe or teach immunoassay restricted to two monoclonals for equivalent quantitative detection of HIV-1 Group M and HIV-2 core proteins, (b) describe or teach immunoassays restricted to two monoclonal antibodies for equivalent quantitative detections of HIV-1 group M, HIV-1 group O, and HIV-2 core proteins, (c) teach methods to overcome monoclonal affinity barriers recognizing cross-reactive antigens leading to non-equivalent detection of HIV-1 group M, O, and HIV core proteins, and (d) high affinity monoclonal antibodies against shared-epitopes as the methods and means to detect diagnostically relevant and equivalent amounts of non-identical core proteins from HIV-1 group M, HIV-2 group O, and HIV-2.
All U.S. patents, patent applications and publications referred to herein are hereby incorporated in their entirety by reference.